The present invention relates to a thinner, more reliable semiconductor package which is fabricated by means of an improved TAB (tape automated bonding) method.
FIG. 1 shows a cross-sectional view of a semiconductor package fabricated by a conventional TAB method. As can be seen in FIG. 1, in accordance with the conventional TAB method, a plurality of bonding pads 13 are formed on predetermined portions of a semiconductor substrate 11, while the remaining portions of the semiconductor substrate 11 are covered with an insulating layer 15. Bumps 19 are formed on the surface of a barrier metal layer 17 formed on the surface of the bonding pads 13. The bumps 19 are connected to one of the ends of inner leads 21 attached to polyimide tape 23, while the other ends of the inner leads 21 are connected to outer leads 25 which are not attached to the polyimide tape 23. Also, a protective layer 27 is formed over the entire surface of the chip, covering a portion of the inner leads 21 bonded to the bumps 19.
After depositing the barrier metal layer 17, a photoresist layer (not shown) is deposited over the entire surface of the chip, and thereafter, the barrier metal layer 17 is exposed by etching the photoresist layer by means of a conventional photolithography process. After forming the bumps 19 on the barrier metal layer 17, the photoresist layer is removed. Subsequently, the bumps 19 and the inner leads 21 of the tape 23 are bonded together, e.g., by means of a thermocompression or reflowing method. Finally, the protective layer 27 is formed over the entire surface of the chip, in order not to expose the portion of the inner leads 21 bonded to the bumps 19.
The conventional TAB method suffers from at least the following shortcomings. If the thermocompression bonding method is used to bond the bumps 19 and the inner leads 21, the inner leads may inadvertently be brought into contact with the edge of the chip by compressive force, thereby resulting in a short-circuit problem. If the reflow-bonding method is used, since the bumps are easily melted and spread out along the inner leads, it is difficult to control the size of the bumps and further, this may cause neighboring pads to be bridged by the spread bumps, thereby also resulting in a short-circuit problem. In addition, it is essential that the protective layer cover the upper surface of the inner leads, thereby unduly limiting the achievable thinness of the package.